1. Field of the Invention
The present invention relates to piezoelectric ceramics and a method of manufacturing the same, an actuator and a method of manufacturing the same, and a printing head and an ink jet printer and, more particularly, to piezoelectric ceramics and an actuator (i.e., multilayer piezoelectric pile) that are suitable for piezoelectric sensors, for example, acceleration sensor, knocking sensor, AE sensor or the like, fuel injector, printing head for ink jet printer, piezoelectric resonator, oscillator, ultrasonic motor, ultrasonic oscillator and filter, and can be advantageously used particularly for a printing head that utilizes vibration of 2-dimensional vibration of expansion and contraction or linear vibration in longitudinal direction or in the direction of the thickness, and a method of manufacturing the same, and a printing head and an ink jet printer.
2. Description of Related Art
Piezoelectric ceramics have been used in, for example, piezoelectric actuator, filter, piezoelectric resonator (oscillator included), ultrasonic oscillator, ultrasonic motor and piezoelectric sensor.
Among these devices, the piezoelectric actuator is used as the positioning piezoelectric actuator for an X-Y stage of semiconductor manufacturing equipment, the actuator for the printing head of ink jet printer or the like, by making advantage of the very high response of the piezoelectric pile to electrical signals, in the order of 10−6 seconds. The ink jet printing head is mounted to various printers wherein characters or images are printed by discharging a drop of ink from a fine ink outlet orifice, recorders, facsimiles, or ink jet printers such as printer used for formation of patterns in the fields of textile printing and ceramic industry.
Piezoelectric ceramics employed in these applications have hitherto been manufactured by directly interposing a ceramic green sheet having several hundreds of μm between a pair of setters made of a porous sintered body, followed by firing.
There is also proposed a method of adjusting flatness of the sintered body in a range from 30 to 100 μm by arranging spacers on a setter base made of the porous material, arranging a setter cover on the spacers to form space, arranging a green sheet in the space, and firing the green sheet while keeping the space formed between the green sheet and the setter cover in a range from 30 to 100 μm (see, for example FIG. 3 of Japanese Unexamined Patent Publication No. 2002-281453).
When the ceramics body thus obtained is applied to a piezoelectric material, since smoothness of ceramics can be set to a given value or less, it is made possible to avoid breakage when an actuator is fixed onto the plane such as metal plate so as to fix into a printer. Therefore, it is preferably used as the actuator for the printing head of ink jet printer or the like, the positioning piezoelectric actuator for and X-Y stage.
However, according to the method of firing the green sheet while interposing between porous materials described in Japanese Unexamined Patent Publication No. 2000-281453, a component that is easy to evaporate through pores is evaporated and significant in-plane variation in composition occurs in case of obtaining an actuator having a thickness of 100 μm or less. It is difficult to control the surface state of the porous material, the resulting piezoelectric ceramics have increased flatness. Furthermore, deposition of particles degranulated from the setter increases flatness and surface roughness of the sintered body.
According to the method of firing the thin green sheet described in Japanese Unexamined Patent Publication No. 2000-281453, a space between the setters and the green sheet is at least 30 μm. Therefore, in case of obtaining an actuator having a thickness of 100 μm or less, flatness of ceramics increases relative to the thickness.
In case of large flatness, since piezoelectric ceramics are stretched so as to correct its curved state into a planar state when an actuator is fixed to a supporting substrate, residual stress is distributed unevenly across the piezoelectric actuator. In the case of an actuator having a thickness of 100 μm or less, comprising a piezoelectric substrate and a plurality of displacement elements provided on the piezoelectric substrate, its piezoelectric constant varies drastically depending on the displacement elements.
Therefore, there have been required to develop piezoelectric ceramics having small flatness and less in-plane variation in piezoelectric constant, and an actuator that has small flatness and also exhibits less in-plane variation in d constant even after bonding on the supporting substrate.
With recent development of multimedia, a non-impact type recording apparatus that employs an ink jet system or a heat transfer system has been developed in place of an impact type recording apparatus, and thus it has been spreading in the fields of various industries and domestic field.
Among these non-impact type recording apparatuses, a recording apparatus that employs an ink jet system has a bright future because of case of multi-gradation and coloration as well as 1 w running cost.
As shown in FIG. 9(a), a printing head that employs an ink jet system has such a structure that a plurality of channels are arranged in parallel as ink flow passages 23a and an actuator is provided on flow passage members 23 formed with partition walls 23b as a wall that partitions the respective ink flow passages 23a (see FIG. 1 of Japanese Unexamined Patent Publication No. 11-34321).
That is, an actuator is bonded with flow passage members 23 so that individual electrodes 26 are disposed right on ink flow passages 23a as openings of flow passages members 23 in an actuator wherein a common electrode 26 are formed on the other side and a plurality of displacement elements 27 are provided.
With such a configuration, a voltage is applied between the common electrode 25 and the individual electrodes 26, thereby to vibrate the displacement elements 27, and thus ink in ink flow passages 23a is compressed and a drop of ink is discharged from ink outlet orifices 28 that open at the bottom of the flow passages members 23.
As shown in FIG. 9(b), a lot of individual electrodes 26 are arranged in parallel on a piezoelectric layer 24 at equal distances to form a printing head provided with a lot of displacement elements 27, thereby making possible to contribute to realize high speed and high accuracy of an ink jet printer.
It has recently been developed about an ink jet printer with high speed and high accuracy. As a result, the displacement element 27 having a close relation with discharge of ink, especially the piezoelectric layer 24 requires thickness reduction and piezoelectric characteristic with high accuracy. Specifically, a photoelectrically actuator with less variation in characteristic is required.
For the purpose of making the thickness of the ceramic layer and the piezoelectric layer uniform, there is made a trial of previously decreasing an amount of a solvent in a slurry for formation of a tape to around ⅓ of the amount of the prior art thereby to reduce variation in thickness during drying, making the thickness of the slurry uniform by passing through a plurality of rolls and subjecting the slurry to the drying step, thus reducing variation in green sheet having thickness of 500 μm (Japanese Unexamined Patent Publication No. 2000-232035).
However, according to the method of decreasing the amount of the solvent described in Japanese Unexamined Patent Publication No. 2000-232035, the slurry for formation of a tape has high viscosity and the tape thus formed has large thickness. Usually, a thick tape having a thickness of several hundreds of micrometers is merely formed because of less shrinkage caused during drying, and a thin tape having a thickness of 50 μm, especially several tens of micrometers can not be formed. To the contrary, the amount of the solvent contained in the slurry for formation of a tape must be increased so as to form a thin tape, and thus variation in thickness occurs during the drying step. Consequently, a thin tape with less variation in thickness can not be formed.
Therefore, a thin laminated piezoelectric pile having a thickness of 100 μm or less with less in-plane variation in thickness is required.